Bearings

ABSTRACT

The specification discloses a hydrostatic bearing in which the channels for the passage of the lubricating fluid are defined between a pair of surfaces clamped together, at least one of the surfaces having been roughened as a result of treatment with a high velocity stream of abrasive particles. A linear, thrust and radial bearing are described.

United States Patent [191 Woolcock Oct. 23, 1973 BEARINGS [75] Inventor:Geoffrey Dennis Woolcoc k,

Oxford, England 31 As q Eve vsi Limi s 221 Filed: Jan.3l, 1972 21 Appl.No: 222,136

52 u.s.c1. 308/9 51 1111.01. ..Fl6c 17/16 58 Field of Search ..308/5,9,122

[56] References Cited UNITED STATES PATENTS 2,368,850 2/1968 7 \yilcox..3031s Primary ExaminerCharles J. Myhre Assistant Examiner-Frank SuskoAttorney-George V. Woodling et al.

[57] I ABSTRACT The specification discloses a hydrostatic bearing inwhich the channels for the passage of the lubricating fluid are definedbetween a pair of surfaces clamped together, at least one of thesurfaces having been roughened as a result of treatment with a highvelocity stream of abrasive particles. A linear, thrust and radialbearing are described.

22 Claims, 5 Drawing Figures Patented Oct. 23, 1973 3,767,277

3 Shoots-Shoot 2 I u uuuunng a 1 BEARINGS BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to a fluid-lubricatedbearing of the type generally referred to as a hydrostatic bearing, thatis to say, a bearing comprising a body having a bearing surface and amember mounted by the bearing for movement relative to, the bearingsurface and in which the member is supported in relation to the bearingsurface by a thin film of bearing fluid which is supplied under pressureto a space between the member and the bearing surface so that the memberis supported by a thin film of bearing fluid at all times whilst thefluid is supplied to the bearing. Such bearings will be referred tohereinafter as of the type described.

One practical embodiment of the bearing of the type described is ajournal bearing but it should be appreciated that the invention can beapplied to other types of bearing such as thrust bearing or a linearbearing, that is a bearing between two surfaces movable rectilinearlyrelative to each other.

2. Description of the Prior Art For convenience the problems encounteredin a conventional hydrostatic journal bearing will now be discussed. 3 I

In the normal construction of a hydrostatic journal bearing the fluid issupplied under pressure through a number'of small radial jet orificesarranged at intervals round the shaft. There is a small clearancebetween the shaft and the bearing surface and in the absence of fluidthe shaft would rest on the bottom surface of the bearing leaving'aclearance at the top. When fluid is supplied the clearance is stillsmaller at the bottom than at the top due to the weight of the shaft andany applied load on the shaft acting vertically downwards and thissmaller clearance caUses the resistance to fluid flow in the region ofsmaller clearance to be greater than in the region of larger clearancethus'increasing the pressure in the fluid at the bottom in relation tothat at the top and thus providing a resultant upward force whichsupports the shaft clear of the bearing surface so that it runs on afilm of fluid. I

With the normal construction of bearing referred to above the jetorifices must be extremely small for any particular dimension ofclearance between the shaft and the bearing. There is an optimum orificediameter which in the case of small bearing clearances may need to be assmall as 0.003 inches. Orifices of this very small size are extremelydifficult to machine and unless a very large number of such orifices isprovided there will inevitably be zones of lower pressure betweenadjacent orifices with consequent reduction in load capacity. The actualdimensions involved will differ according to whether the fluid used isliquid or a gas but the overall problam is the same.

Similar problems are encountered in other types of hydrostatic bearingsuch as a thrust or a linear bearing.

SUMMARY OF THE INVENTION An object of the invention is to provide a newand improved hydrostatic bearing of the type described wherein the abovementioned problems are overcome or are reduced.

According to the present invention I provide a hydrostatic bearingcomprising a body having a bearing surface and a member mounted by thebearing for movement relative to the bearing surface and in which themember is supported in relation to the bearing surface by a thin film ofbearing fluid which is supplied under pressure to a space between themember and the hearing surface so that the member is supported by thefluid film at all times whilst bearing fluid is supplied under saidpressure to the bearing, including the improvement wherein the body isformed with channels for the passage of bearing fluid, said channelsextending to said space between the member and the bearing surface andare defined between a pair of complementary surfaces on first and secondbody parts maintained in fixed relationship to each other, said firstand second body parts being impervious to the passage of bearing fluid,and at least one of which surfaces is roughened to provide a pluralityof evenly and randomly distributed pits, substantially all of said pitsbeing interconnected to adjacent pits to permit flow of bearing fluidtherebetween, said pits constituting said bearing fluid channels.

The bearing may be a journal bearing and the member may be a cylindricalshaft and said bearing surface may define a cylindrical surface ofslightly larger diameter than the diameter of said shaft within whichsaid shaft is disposed and said channels may extend between a plenumchamber. and said cylindrical surface and may be defined between a pairof annular flat surfaces maintained in fixed relationship to each other,at least one of which surfaces has been roughened as a result oftreatment with a high velocity stream of abrasive particles.

Alternatively, the bearing may be a thrust bearing wherein the memberhas an end surface extending transversely of the axis of rotation of themember and wherein the body has a portion thereof defining a bearingsurface of a shape complementary to the end surface of the member, andwherein said air feed channels extend to the space between said endsurface and the bearing surface .ata position spaced inwardly of theouter periphery of the bearing surface of the body.

Alternatively, the bearing may be a linear bearing and said body mayinclude a rectilinearly extending bearing surface and said member havinga bearing surface of complementary configuration and wherein saidsurfaces defining said air feed channels in the body extend in thedirection of relative movement between the member and the body.

The surfaces may be held together under pressure.

Such a construction gives a multiplicity of small channels which takethe place of the jet orifices referred to above and which permit a muchmore uniform distribution of fluid around the shaft. The channels areprovided by a plurality of evenly and randomly distributed pits ofvarying size, substantially all of the pits being inter-connected toadjacent pits to permit flow of fluid therebetween. In addition, themechanical treatment necessary to obtain these channels is greatlysimplified since it is merely a question of roughening the respectivesurface or surfaces to a sufficient extent to provide the required sizeof channel. If subsequently the channels tend to become clogged withdirt it is then only necessary to dismantle the assembly, to clear theroughened surface and then to reassemble the bearing again.

The actual size of channel required, and hence the size of the pitswhich is required, and hence the degree of roughening necessary isdependent on the overall characteristics of the bearing, that is to say,the diameter of the shaft, the width of the clearance between the shaftand the bearing surface, the available supply pressure of the fluid tobe used, and the viscosity of the fluid. The desired size of pit isobtained by appropriate selection of the size and velocity of theabrasive particles and the duration of the treatment. Basically theroughening treatment is similar to the well known sandblasting orshot-blasting processes. In such processes the stream of abrasiveparticles which term for the purposes of the present specification isused to include the use of steel shot is directed at an angle of forexample, 45 to the workpiece. This has both a roughening and a cuttingaction. The impact of the particles on the surface being treated tendsto displace the material of the surface and to form it into adjacentridges and depressions. Since the movement of the stream of particleshas a component parallel to the surface, however, there is an overallsweeping effect and material tends to be displaced towards one edge ofthe material and eventually to be removed from that edge. Although thisconventional form of blasting process can be used for the roughening ofa surface in accordance with the present invention it has been foundthat improved results are obtained if the stream of particles isdirected normally. Under these circumstances there is no component ofthe motion parallel with the surface so that there is no tendency formaterial to be removed and the effect is merely to accentuate thedisplacement of material to define adjacent ridges and depressions. Inorder to maintain uniform treatment the surface may be rotated in theblast stream.

It has been found in practice that much improved results are obtained ifthe material is treated with abrasive particles to a greater extent thanthat necessary to produce the desired size of channels and the materialis then lapped with a suitable abrasive material to reduce the size ofthe pits so as to give the precise size of channels required. Thisenables a much more precise control to be maintained over the form ofthe channels and hence over the characteristics of the bearing.

If the material being roughened is steel the effect of the treatment isto introduce a measure of workhardening which is advantageous inprolonging the life of the component. Other metals than steel can beused, however, and even non-metallic materials such as hard ceramicswhich are found to give particularly good results. I

The channels for the passage of the lubricating fluid may either bedefined between one roughened surface and one flat surface or betweentwo roughened surfaces, the choice between these two alternativesdepending on the required size of channel and the extent to which asingle surface can conveniently be roughened by the blasting treatment.If the required depth of channel can be obtained merely by rougheningone of the surfaces there is no advantage in treating both surfaces andthe engaging surface may be left flat.

In order to provide the engaging surfaces defining the channels the bodyportion of the bearing must be formed as at least two parts divided fromone another. The engaging surfaces of either one or both these parts arethen required to be roughened. As a matter of convenience, however, theroughening may be applied to a component of the body portion which issandwiched between other components. This provides two pairs of engagingsurfaces and the component in question may be roughened on one or bothof its faces. In a particular construction two such components aresituated towards opposite ends of the body portion.

BRIEF DESCRIPTION OF THE DRAWINGS Constructions of bearing in accordancewith the invention will now be described in more detail by way ofexample with reference to the accompanying drawings in which FIG. 1 isan exploded perspective view of one construction of journal bearingembodying the invention.

FIG. 2 is an axial sectional view of the assembled bearing of FIG. 1.

FIG. 3 is an axial sectional view of a modified construction of journalbearing embodying the invention,

FIG. 4 is an exploded perspective view of one construction of linearbearing embodying the invention,

FIG. 5 is a perspective view of one construction of a rotary thrustbearing embodying the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Turning first to FIG. 1, the bodyportion of the bearing comprises'a main central part 1, and end parts 2and 3. Between these are sandwiched relatively thin plates 4 and 5which, as illustrated, are roughened as hereinafter to be described onboth sides but may, if required, be roughened on only one side. When theplates are roughened on both sides a total of four sets of channels forthe passage of fluid are provided so that no roughening is required tothe main body portions 1, 2 and 3. All the components so far describedare formed with bolt holes 11 and FIG. 2 shows the components assembledand held together by bolts 12.

In the view of FIG. 2 a shaft 13 is shown in position in the bearing andfor simplicity of illustration the clearance 14 at the bottom is shownas equal to that 15 at the top. In practice, when the bearing is not inoperation i.e., when no fluid is being supplied to the bearing therewould be no clearance 14 at the bottom at all and when operating theclearance 14 would be smaller than that 15 for the reasons alreadydescribed. The assembly of parts 1, 2 and 3 together with the plates 4and 5 is surrounded by an outer jacket 17 formed with an internal slot18 communicating with circumferential grooves 19 and 20 encircling theplates 4 and 5. The Slot 18 together with the grooves 19 and 20 definesa plenum chamber to which fluid under pressure is supplied by way of aconnection 21. From there the fluid flows inwardly along the channelsdefined between the roughened surface of the plates 4 and 5 and thesmooth engaging surfaces of the parts 1, 2 and 3. Since the grooves 19and 20 completely encircle the plates 4 and 5 there is a uniform flow offluid.

The fluid may be a liquid, for example, oil, or a gas, for example, air.

The degree of roughening of the plates 4 and 5 is selected in accordancewith the fluid to be used and also in accordance with the othervariables described hereinbefore.

The plates are roughened by treatment with abrasive particles asdescribed hereinbefore.

The end pressure exerted by the bolts 12 tends to press the ridgesformed in the roughened surfaces of the plates 4 and 5 into the engagingsurfaces on the parts 1, 2 and 3, thus tending to interlock thesecomponents and avoiding the need for the provision of dowels orregisters which would otherwise be necessary in order to preventrelative movement of the components.

The avoidance of such dowels or registers represents a majorsimplification in that they are notoriously difficult to manufacture tothe required degree of accuracy. In the bearing shown in FIG. 3 theconnection 21 is duplicated to supply two separate plenum chambers 25from which fluid flows inwardly along four separate sets of channelsdefined by the roughened surfaces on opposite sides of plates 26 whichare rather thicker than the plates 4 and 5. The plates 26 are spacedapart by a distance considerably greater than their own thickne'sses.Such an assembly is suitable for use with a grinding spindle, forexample. Owing to the length of the assembly, central exhaust outlets 27are connected proportions, of FIGS. 1 and 2.

Inches Shaft diameter 2 Bearing length 2 Radial clearance between dhaftand bearing 0.0007 Distance between plates 4 and 5 1 Outside diameter ofbearing 3 The plates 4 and 5 were made of rust resisting steel and thesurfaces were roughened by treatment with 250 micron-sized abrasiveparticles directed normally to the surface for a period of seconds witha propellant air pressure of 80 p.s.i.

The roughened surfaces comprises a large number of pits of varying sizewhich are evenly and randomly distributed over the roughened surfaceswith substantially all of the pits breaking into adjacent pits or beingbroken into by adjacent pits whereby the bearingfluid can flow throughthe pits. The pits were approximately 0.001 in. to 0.003 in. deep, andof approximately 0.00001 sq. in. to'0.00008 sq. in. in area.

In operation the pressure applied dependson the nature of the fluid, butwhen using air a typical pressure is 80 p.s.i. and when using oil atypical pressure is 200 300 p.s.i.

By way of a second example the dimensions and manufacturing sequence fora bearing having the construction, but not the proportions, of FIG. 3will now be described.

Two rings 3 inches outside diameter X 2 inches inside diameter X kinches thick are machined with ground faces, four holes drilled andcounterbored to suit cap head screws. One tube 3 inches outside diameterX 2 inches inside diameter X 5 inches long is machined with groundfaces, four tapped holes each end and one exhaust hole in the centre.Two rings 3 inches outside diameter X 2 inches inside diameter X 1 inchthick are machined with ground faces, four clearance holesfor I nent. Itis blasted at 20 p.s.i. for 20 seconds using a 250 micron-sizedabrasive. This process is repeated for the other side of the rings. Pitsof the same nature as described in the first example were produced.

After blasting, the faces are lapped to give an air flow of 35 cubicfeet per hour at p.s.i. through each of the channels, defined by theshot blasted faces, when all five components are bolted together. Afterlapping the pits were approximately 0.0004 inch to 0.001 inch deep andapproximately 0.00001 sq.in. to 0.00008 sq.in. in area.

The bore is then honed to size holding a tolerance of 0.0001 inch. Theunit is then stripped down, cleaned, all fraze removed and reassembledusing an expanding mandrel.

A shaft is produced 8 inches long with two journals 2 inches long at theends, the diameter being 0.0012 inch less than the bore diameter of thebearing, the centre 4 inches being 0.040 inch smaller. The bearing isthen assembled into a housing fitted with air feed holes to each pair ofchannels. The shaft, when the air feed pressure is 80 p.s.i., will carrya static load of 270 lbs. at a deflection rate of 470,000 lbs/inch.

By way of a third example the dimensions and manufacturing sequence foranother bearing having the construction, but not the proportions, ofFIG. 3 will be described. I

Two rings 4 inches outside diameter X 3 inches inside diameter X /4 inchthick are machined with ground faces, four holes drilled andcounterbored to suit cap head screws. One tube 4 inches outside diameterX 3 inches inside diameter X 7% inches long is machined with groundfaces, four tapped holes each end and one exhaust hole in the centre.Two rings made of stainless steel and of 4 inches outside diameter X 3inches inside diameter X 1 /2 inches thick are machined with groundfaces, four clearance holes for screws.

The two 1% inches thick rings are then placed on a turntable and rotatedat rev. per min. in a shot blasting cabinet, the nozzle being 8 inchesabove the component. It is blasted at 20 p.s.i. for 30 seconds using a250 micron size abrasive. The process is then repeated for the otherside of the rings.

After blasting, the faces are lapped to give an air flow of 4 inchescubic feet per hour at 80 p.s.i. through each of the channels, definedby the shot blasted faces, when all five components are bolted together.The pits produced after blasting and lapping were as described inexample 2. I

The bore is then honed to size holding a tolerance of 0.0001 inch. Theunit is then stripped down, cleaned, all fraze removed and reassembledusing an expanding mandrel.

A shaft is produced 12 inches long with two journals 3 inches long atthe ends, the diameter being 0.0012 inch less than the bore diameter ofthe bearing, the centre 6 inches being 0.040 inch smaller. The bearingis then assembled into a housing fitted with air feed holes to each pairof channels. The shaft, when the air feed pressure is 80 p.s.i. willcarry a static load of 600 lbs. at a deflection rate of 1,000,000lbs/inch.

It will be understood that the constructions described above are merelyexamples of a wide variety of constructions in accordance with theinvention. In the simplest version, the body of the bearing is made ofonly two portions to provide a single set of channels. This basicconstruction can be doubled after the manner of that of FIG. 3, as canalso the construction of FIGS. 1 and 2. Similarly, one half of theconstruction of FIG. 3 can be used as a single short bearing. For a verylong bearing any required number of sets of channels can be achieved byuse of an appropriate number of body components.

By way of a fourth example a linear bearing shown in FIG. 4 will now bedescribed. The bearing comprises a base member 40 which may be of anydesired external configuration and which is provided with a U-sectionchannel 41 therein to receive a sliding body 42. The sliding body 42 isof generally T-shape in cross section, having two rebates 43 formedalong its two lower sides. The rebates 43 receive square elongatedmembers 44 made of stainless steel, which are secured to the body 42 byscrews 45. Two adjacent faces 44a of the elongated members 44 are shotblasted, as to be described hereinafter, and these shot blasted facesare maintained urged into contact with the faces of the rebates 43 bythe screws 45. A central longitudinally extending passage 46 is formedin part of the body 42 and transversely extending passages 47 areprovided to extend from the passage 46 to the corners of the rebates 43.

Intermediate their ends the square section members 44 have a chamferedportion 48 which, in conjunction with the corner of the rebate 43,provides a chamber for air feed thereto from the central feed passage 46via the transverse passages 47.

The diagonally opposite corner of each elongated member 44 is alsochamfered as shown at 49 to provide an exhaust chamber and smallclearance spaces are provided between the sliding body 42 and the basemember 40 in the regions indicated at 50.

Longitudinally extending retaining members 51 are provided, secured tothe member 40 by screws 52 to retain the sliding body 42 in position. Ifdesired, further fluid feed channels can be provided on the body toprovide a hydrostatic bearing between the body 42 and the retainingmembers 51.

In use, air under pressure is fed into the central passage 46 and thenenters the chambers formed by the chamfered parts 48 through thetransversely extending passages 47. The air then passes through the finechannels provided by the shot blasted surfaces 44a of the elongatedmembers 44 to the bearing faces and then the air exhausts either througha central exhaust passageway 53 or through the passage ways provided bythe other chamfered edges 49, or upwardly to escape from the top of thebody.

In this case the faces 44a of the elongatedmembers 44 are shot blastedin a manner similar to that desribed hereinbefore in connection with thesecond and third examples, i.e., they are shot blasted with a nozzleabout 8 inches above the component, so that the shot is directednormally upon the component and are blasted at about 20 p.s.i., using acoarse grain abrasive of controlled size. During this shot blastingoperation the elongated members are reciprocated backwards and forwardsin front of the nozzle for appropriate lengths of time to give thedesired depth of passage.

After blasting, the faces are lapped to give an air flow of about cubicfeet per hour per square inch of treated surface at 80 p.s.i. Again thepits produced were as described in example 2.

It will be appreciated that each surface of the elongated members to beshot blasted is shot blasted separately, the component 44 being turnedthrough 90 at the end of each shot blasting operation.

By way of a fourth example, a rotary thrust bearing is described inconnection with FIG. 5, and this rotary thrust bearing also acts as aradial bearing.

In this embodiment, referring now to FIG. 5, the bearing comprises afixed body 60 of disc configuration having an axially extendingcylindrical boss 61 formed integrally therewith. An annular member 62 ofsquare cross section is secured to the member 60 in the shoulder formedbetween the member 60 and the boss 61 and is secured in position byscrews, not shown. An axially directed feed passage 64 is formed in thebody 60 and radially extending feed passages 65 radiate therefrom to thecorner 66 between the boss part 61 and the annular member 62. v

The annular member 62 has two of its adjacent surfaces shot blasted, asto be described hereinafter, and the corner between the shot blastedsurfaces is chamfered, as indicated at 66.

A rotatable member 67 is of generally cylindrical configuration, havinga generally cylindrical recess 68 formed therein which receives thefixed body 60. A central shallow recess 69 is formed in the rotatablemember 67 and an exhaust passage 70 is formed therein.

In use, air under pressure is fed into the feed passage 64 and via thepassages 65 to the chamber formed by the chamfered part 66 and thenthrough the channels formed by the shot blasted surfaces of the annularmember 63, and hence into the bearing surfaces between the fixed member60 and the rotatable member 67. The air from the bearing surfacesexhausts from the bottom of the bearing in the region indicated at 74and via the exhaust passages 70 and 75.

The shot blasting operation on the annular member is performed in asimilar manner to the examples described hereinbefore.

So far as the annular surface is concerned, this is shot blasted byplacing the annular member on a turntable and rotating at I40 revs. perminute in a shot blasting cupboard, with the nozzle being placed 8inches above the component. It is blasted at 20 p.s.i. for anappropriate period of time to give the desired depth of passage, using acoarse grain abrasive of controlled size.

For the internal, cylindrical, surface of the annular ring, the surfacemay either be shot blasted with a nozzle placed within the annulus sothat the shot is directed normally on to the surface, in which case thedistance between the nozzle and the surface will be less than 8 inches,and hence a corresponding lower pressure and time will be used oralternatively the shot may be directed onto the surface at an angle froma nozzle placed externally of the annular ring so that in this case theshot will be directed on to the surface at a slight angle.

Again, after blasting, the faces are lapped to give an air flow of about10 cubic feet per hour per square inch of treated surface at p.s.i.through the channels. The pits produced were as described in example 2.

It will be appreciated from the above examples that the terms body andmember" are used herein to refer to the relatively moving parts of abearing, and that the term body is not used exclusively to refer to apart of the bearing which is fixed relative to the surroundings, not isthe term member used exclusively to refer to the part which is movablerelative to the surroundings.

All the component parts of the bearings, with the exception of the feedchannels, are, of course, impervious to the passage of the bearingfluid.

What we then claim is:

l. A hydrostatic bearing comprising a body having a bearing surface anda member mounted by the bearing for movement relative to the bearingsurface and in which the member is supported in relation to the bearingsurface by athin film of bearing fluid which is supplied under pressureto a space between the member and the bearing surface so that the memberis supported by the fluid film at all times whilst bearing fluid issupplied under said pressure to the bearing, including the improvementwherein the body is formed with channels for the passage of bearingfluid, said channels extending to said space between the member and thebearing surface and are defined between a pair of complementary surfaceson first and second body parts maintained in fixed relationship to eachother, said first and second body parts being impervious to the passageof bearing fluid, and at least one of which surfaces is roughened toprovide a plurality of evenly and randomly distributed pits,substantially all of said pits being interconnected to adjacent pits topermit flow of bearing fluid therebetween, saids pits constituting saidbearing fluid channels. I

2. A bearing according to claim 1, wherein the bearing is a journalbearing and the member is a cylindrical shaft and wherein said bearingsurface defines a cylindrical surface of slightly larger diameter thanthe diameter of said shaft and within which cylindrical surface saidshaft is disposed and wherein said channels extend between aplenumchamber and said cylindrical surfaces and are defined between a pair ofannular flat surfaces maintained in fixed relationship to each other.

3. A'bearing according to claim 2, wherein said surfaces are heldtogether under axial pressure.

4. A bearing according to claim 3, in which each roughened surface isformed on a component of the body in the form of an annular plate, whichcomponent is sandwiched between othercomponents.

5. A bearing according to claim 1, wherein the bearing is a thrustbearing and wherein the member has an end surface extending transverselyof the axis of rotation of the member and wherein the body has a portionthereof defining a bearing surface of a shape complementary to the endsurface of the member, and wherein said channels extend to the spacebetween said end surface and the bearing surface at a position spacedinwardly of the outer periphery of the bearing surface of the body.

6. A bearing according to claim 5, wherein said complementary surfacesbetween which said channels are defined are of cylindrical configurationand are coaxial with the axis of rotation of the member.

7. A bearing according to claim 6, wherein the body comprises a coremember of stepped cylindrical configuration, having one part of a largerdiameter than another part of a smaller diameter, and there being ashoulder extending radially outwardly from the periphery of the smallerdiameter part, and there being a ring member having two adjacentsurfaces mutually inclined at right angles and positioned on saidshoulder, said adjacent surfaces of the ring member being positioned soth'atone surface, of cylindrical configuration,v

is positioned adjacent the wall of the smaller diameter part of the coremember whilst the other surface, of annular configuration, is positionedadjacent said shoulder, and wherein the wall of the smaller diameterpart and the cylindrical wall of the ring member define said feedchannels therebetween.

8. A bearing according to claim 5, wherein the bearing is a combinationthrust and journal bearing, the member including a cylindrical portionadapted to encircle a portion of the body and wherein second bearingfluid channels are provided extending from a pienum' chamber to thespace between the cylindrical portion and the body, and said secondchannels being defined between a pair of complementary surfacesmaintained in fixed relationship to each other, at least one of saidsurfaces being roughened to provide a plurality of evenly and randomlydistributed pits, substantially all of said pits being interconnected toadjacent pits to permit flow of bearing fluid therebetween, said pitsconstituting said second bearing fluid channels.

9. A bearing according to claim 8, wherein said second channels aredefined between surfaces of annular configuration and lying in a planenormal to the axis of rotation of the member.

10. A bearing according to claim 1, wherein the bearing is a linearbearing and said body includes a rectilinearly extending bearing surfaceand said member has a bearing surface of complementary configurationthereto and wherein said surfaces defining said channels in the bodyextend in the direction of relative movement between the member and thebody.

11. A bearing according to claim 10, wherein said surfaces between whichsaid channels are defined are planar and extend normal to said bearingsurfaces.

12. A bearing according to claim 11, wherein the body has a core parthaving longitudinally extending shoulders on opposite sides thereof, thesurfaces of the core part defining each shoulder including a surfacewhich extends normal to said bearing surfaces and wherein an elongatemember having two mutually inclined adjacent surfaces is positioned ineach of said shoulders, and wherein said surfaces and. the surfaces ofthe elongate members adjacent thereto comprise said surfaces definingthe feed channels.

13. A bearing according to claim 10, wherein the body is provided withsecond bearing fluid channels extending transversely of the body normalto the first mentioned channels and being defined between a pair ofcomplementary surfaces maintained in fixed relationship to each other,at least one of said surfaces being roughened to provide a plurality ofevenly and randomly distributed pits, substantially all of saidpitsbeing interconnected to adjacent pits to permit flow of bearing fluidtherebetween, said pits constituting said second bearing fluid channels.

14. A bearing according to claim 1, wherein the or at least one of theroughened surfaces has been lapped.

15. A bearing according to claim 1, wherein the pits have a depth lyingin the range from 0.004 in. to 0.003

16. A bearing according to claim 1, wherein the pits have an area lyingin the range from 0.00001 sq. in. to 0.00008 sq. ins.

17. A method of manufacturing a fluid lubricated hydrostatic bearing asclaimed in claim 1, including the steps of subjecting a surface of acomponent of the bearing to treatment with a high velocity stream ofvelocity stream of abrasive particles.

20. A method according to claim 17 wherein the pits have a depth lyingin the range from 0.0004 in. to 0.003

21. A method according to claim 17 wherein the pits have an area lyingin the range from 0.00001 sq. in. to 0.00008 sq.in.

22. A bearing according to claim 1 wherein said first and second bodyparts are made of metal.

1. A hydrostatic bearing comprising a body having a bearing surface and a member mounted by the bearing for movement relative to the bearing surface and in which the member is supported in relation to the bearing surface by a thin film of bearing fluid which is supplied under pressure to a space between the member and the bearing surface so that the member is supported by the fluid film at all times whilst bearing fluid is supplied under said pressure to the bearing, including the improvement wherein the body is formed with channels for the passage of bearing fluid, said channels extending to said space between the member and the bearing surface and are defined between a pair of complementary surfaces on first and second body parts maintained in fixed relationship to each other, said first and second body parts being impervious to the passage of bearing fluid, and at least one of which surfaces is roughened to provide a plurality of evenly and randomly distributed pits, substantially all of said pits being interconnected to adjacent pits to permit flow of bearing fluid therebetween, saids pits constituting said bearing fluid channels.
 2. A bearing according to claim 1, wherein the bearing is a journal bearing and the member is a cylindrical shaft and wherein said bearing surface defines a cylindrical surface of slightly larger diameter than the diameter of said shaft and within which cylindrical surface said shaft is disposed and wherein said channels extend between a plenum chamber and said cylindrical surfaces and are defined between a pair of annular flat surfaces maintained in fixed relationship to each other.
 3. A bearing according to claim 2, wherein said surfaces are held together under axial pressure.
 4. A bearing according to claim 3, in which each roughened surface is formed on a component of the body in the form of an annular plate, which component is sandwiched between other components.
 5. A bearing according to claim 1, wherein the bearing is a thrust bearing and wherein the member has an end surface extending transversely of the axis of rotation of the member and wherein the body has a portion thereof defining a bearing surface of a shape complementary to the end surface of the member, and wherein said channels extend to the space between said end surface and the bearing surface at a position spaced inwardly of the outer periphery of the bearing surface of the body.
 6. A bearing according to claim 5, wherein said complementary surfaces between which said channels are defined are of cylindrical configuration and are co-axial with the axis of rotation of the member.
 7. A bearing according to claim 6, wherein the body comprises a core member of stepped cylindrical configuration, having one part of a larger diameter than another part of a smaller diameter, and there being a shoulder extending radially outwardly from the periphery of the smaller diameter part, and there being a ring member having two adjacent surfaces mutually inclined at right angles and positioned on said shoulder, said adjacent surfaces of the ring member being positioned so that one surface, of cylindrical configuration, is positioned adjacent the wall of the smaller diameter part of the core member whilst the other surface, of annular configuration, is positioned adjacent said shoulder, and wherein the wall of the smaller diameter part and the cyliNdrical wall of the ring member define said feed channels therebetween.
 8. A bearing according to claim 5, wherein the bearing is a combination thrust and journal bearing, the member including a cylindrical portion adapted to encircle a portion of the body and wherein second bearing fluid channels are provided extending from a plenum chamber to the space between the cylindrical portion and the body, and said second channels being defined between a pair of complementary surfaces maintained in fixed relationship to each other, at least one of said surfaces being roughened to provide a plurality of evenly and randomly distributed pits, substantially all of said pits being interconnected to adjacent pits to permit flow of bearing fluid therebetween, said pits constituting said second bearing fluid channels.
 9. A bearing according to claim 8, wherein said second channels are defined between surfaces of annular configuration and lying in a plane normal to the axis of rotation of the member.
 10. A bearing according to claim 1, wherein the bearing is a linear bearing and said body includes a rectilinearly extending bearing surface and said member has a bearing surface of complementary configuration thereto and wherein said surfaces defining said channels in the body extend in the direction of relative movement between the member and the body.
 11. A bearing according to claim 10, wherein said surfaces between which said channels are defined are planar and extend normal to said bearing surfaces.
 12. A bearing according to claim 11, wherein the body has a core part having longitudinally extending shoulders on opposite sides thereof, the surfaces of the core part defining each shoulder including a surface which extends normal to said bearing surfaces and wherein an elongate member having two mutually inclined adjacent surfaces is positioned in each of said shoulders, and wherein said surfaces and the surfaces of the elongate members adjacent thereto comprise said surfaces defining the feed channels.
 13. A bearing according to claim 10, wherein the body is provided with second bearing fluid channels extending transversely of the body normal to the first mentioned channels and being defined between a pair of complementary surfaces maintained in fixed relationship to each other, at least one of said surfaces being roughened to provide a plurality of evenly and randomly distributed pits, substantially all of said pits being interconnected to adjacent pits to permit flow of bearing fluid therebetween, said pits constituting said second bearing fluid channels.
 14. A bearing according to claim 1, wherein the or at least one of the roughened surfaces has been lapped.
 15. A bearing according to claim 1, wherein the pits have a depth lying in the range from 0.004 in. to 0.003 in.
 16. A bearing according to claim 1, wherein the pits have an area lying in the range from 0.00001 sq. in. to 0.00008 sq. ins.
 17. A method of manufacturing a fluid lubricated hydrostatic bearing as claimed in claim 1, including the steps of subjecting a surface of a component of the bearing to treatment with a high velocity stream of abrasive particles for a length of time sufficient to produce the required degree of roughening so that the surface, in co-operation with a surface of another component of the bearing, defines feed channels for the lubricating fluid of the bearing.
 18. A method according to claim 17, wherein the stream of abrasive particles is directed substantially normally to the surface.
 19. A method according to claim 17, wherein the surface is lapped subsequent to said treatment with a high velocity stream of abrasive particles.
 20. A method according to claim 17 wherein the pits have a depth lying in the range from 0.0004 in. to 0.003 in.
 21. A method according to claim 17 wherein the pits have an area lying in the range from 0.00001 sq. in. to 0.00008 sq.in.
 22. A bearing according to claim 1 wherein said first and sEcond body parts are made of metal. 